用硅烯醚型引发剂进行的基团转移聚合

本文报道了一类硅烯醚型的基团转移聚合引发剂。并以负离子和HgI_2等为催化剂,进行了甲基丙烯酸酯和丙烯酸酯的基团转移聚合。得到了实测分子量和理论分子量相近且分散性较小的浆合物。进行了甲基丙烯酸甲酯的活性聚合以及其与丙烯酸酯的A-B-A型三嵌段共聚,证实具有活性高分子的特征。探讨了该类引发剂引发基团转移聚合的机理,研究了催化剂和引发剂的配合选择性以及催化剂和引发剂的摩尔比对产物分子量和转化率的影响,发现该类引发剂引发的基团转移聚合是一恒速聚合反应。     

用大分子引发剂法制备嵌段共聚物

主要介绍了用大分子引发剂法制备嵌段共聚物的方法。大分子引发剂是从已商品化的功能聚合物制得或用其它活性聚合方法合成。从单封端的端羟基聚合物、其它单官能团或双官能团聚合物以及双功能基团缩聚物制得大分子引发剂．然后用于原子转移自由基聚合(ATRP)、氮氧稳定自由基聚合以及可逆加成裂解链转移(RAFT)聚合等．可制得结构可控、分子量分布窄的嵌段共聚物。     

四乙基二氟化氢铵催化的基团转移聚合

用三种引发剂进行了二氟化氢负离子催化的基团转移聚合,得到了窄分布的,实测分子量和理论分子量相近的一系列聚甲基丙烯酸酯产物,合成了分子量达20万以上的聚甲基丙烯酸甲酯,探讨了引发剂和催化剂用量对产物的分子量和分散性的影响,认为过量的催化剂使产物的分散性加大和实测(?)_n大于理论M_n。得到了控制聚合的最佳催化剂和引发剂浓度比。     

催化剂对基团转移聚合的影响

本文研究了催化剂的种类和用量对硅烯醚型引发剂引发的基团转移聚合的影响。发现四丁基二苯甲酸氢铵(Bu_4NH(C_6H_5CO_2)_2,TBABB)和HsI_2的催化效果较好。只需引发剂的4％的HgI_2即可使MMA的基团转移聚合达到完全转化。认为有效的氧负离子催化剂应由较稳定的铵正离子和电负性较大的氧负离子所组成。过量的催化剂不利于基团转移聚合的进行。考察了TBABB催化剂对温度的依赖性及其浓度对聚合速率,分子量和分子量分布,转化率的影响。     

(n-BuCp)_2TiCl_2/Sn/I_s引发合成梳形羟基功能化无规聚苯乙烯及聚合物结构与性能的研究

采用茂金属化合物(n-BuCp)2TiCl2,还原剂(Sn),引发剂苯基缩水甘油基醚甲醛共聚物(Is)组成的催化体系引发苯乙烯活性自由基聚合,合成梳形羟基功能化无规聚苯乙烯.考察了聚合温度、聚合时间及引发剂与单体的比例对苯乙烯聚合的影响.当聚合温度在65～95℃范围内,随着聚合温度的升高,聚合物的分子量及单体转化率增加;在一定温度下,聚合物的分子量与单体转化率之间存在线性增长关系,且聚合物的分子量分布较窄(Mw/Mn=1.6～1.9).采用GPC,WAXD,13C(1H)-NMR对聚合物(沸丁酮可溶级分)的结构与性能进行了表征.GPC结果证明(n-BuCp)2TiCl2/Sn/Is引发苯乙烯聚合为活性聚合;13C-NMR和WAXD结果说明聚苯乙烯链段为无规结构;1H-NMR结果表明聚合物分子链中含有羟基,并根据其结果计算出聚合物分子的臂数为4,与引发剂Is的环氧基团数相等.这些结果证明了其聚合机理是经环氧基团开环后形成的自由基引发苯乙烯自由基聚合.     

HES/TiCl_4体系引发异丁烯可控正离子聚合

由六官能团引发剂环氧化角鲨烯(HES)与TiCl4组成引发体系,引发异丁烯(IB)在CH2Cl2/n-Hex(40/60,V/V)混合溶剂中进行正离子聚合,分别探讨了HES和2,6-二甲基吡啶(DMP)用量对IB正离子聚合转化率、产物分子量及其分布的影响.结果表明HES和微量水均可与TiCl4发生络合,并分别形成碳正离子和质子两种引发活性中心,导致聚合产物GPC谱图呈明显双峰分布.增加引发剂HES用量([HES]=2.64mmol/L),可以减少聚合体系中微量水的不可控引发,提高HES引发效率;在聚合体系中引入少量DMP时,可明显地减少微量水的不可控引发和提高HES的引发效率,使得即使在较低HES用量下([HES]=0.084mmol/L),也可达到主要由HES引发IB正离子聚合,制备出官能叔氯末端的六臂星形支化遥爪聚异丁烯,GPC谱图呈现单峰分子量分布,分布指数为1.5左右.     

一种大分子引发剂的引发作用研究

将溶液聚合合成的α-甲基苯乙烯(AMS)和甲基丙烯酸缩水甘油酯(GMA)的低相对分子质量共聚物(计为PAG)作为大分子引发剂,分别研究了PAG引发单体甲基丙烯酸甲酯(MMA)和苯乙烯(St)的本体聚合反应,采用GPC和FTIR等手段对聚合产物进行了表征.研究结果表明,在加热到一定温度时,PAG具有引发作用,可以引发MMA和St进行本体聚合反应;聚合产物具有再引发功能,且其分子量与聚合物产率和聚合反应时间之间均有较好的线性关系.     

DCC/AlCl_3体系引发异丁烯正离子聚合

研究以对-二枯基氯(DCC)/AlCl3体系引发异丁烯在CH2Cl2/Hex(40/60,V/V)混合溶剂中进行正离子聚合,探讨了DCC用量、给电子试剂,如三苯胺(TPA)、2,6-二甲基吡啶(DMPy)对异丁烯正离子聚合转化率、产物分子量及其分布的影响.结果表明,在无给电子试剂存在时,DCC和体系中微量水均可与AlCl3产生络合竞争引起相继的引发竞争,聚合产物GPC谱图呈双峰分布,分子量分布宽,需要大量的引发剂DCC(DCC/H2O=5.3)来减少体系中微量水的不可控引发;在少量上述给电子试剂存在下,可提高DCC的引发效率,减少向单体链转移反应,提高聚合产物的分子量和使分子量分布呈较窄的单峰分布,即使在较低DCC用量下也可基本抑制体系中微量水的不可控引发,达到DCC定量引发,并得到分子量分布相对较窄(Mw/Mn≈2.3)的聚异丁烯产物.     

碳—碳键新型引发剂的研究

α-氰基苯乙酸乙酯用Cu~( )-TMEDA-O_2进行氧化偶联反应,产物经色谱或重结晶法分离,经红外光谱、紫外光谱、~1H核磁共振谱、质谱、元素分析鉴定及其碱性水解产物等认定为内消旋-2,3-二氰基-2,3-二苯基丁二酸二乙酯(Ⅰ).用Ⅰ引发苯乙烯进行本体聚合,测定了聚合温度和Ⅰ的用量对苯乙烯的转化率～时间曲线的影响,测定了各种条件下所得聚苯乙烯的分子量及其分散系数.1是一种既有效又安全的碳—碳键型引发剂.     

醇铁化合物引发丙交酯开环聚合的研究

分别以乙醇铁、正丙醇铁、异丙醇铁、正丁醇铁为引发剂进行D,L-丙交酯和L-丙交酯的本体开环聚合,研究了在130℃的聚合温度下引发剂用量和聚合时间对聚合反应的影响.结果表明这些醇铁化合物对丙交酯开环聚合都有较好的引发作用;聚合36h,单体转化率可达90%以上.单体转化率在引发剂/单体摩尔比为1/1000时最高,然后随引发剂用量增加和聚合时间延长而降低.乙醇铁表现出最高的引发活性,聚合产物的相对粘均分子量最高可达7·28×104[聚(D,L-丙交酯)]和19·00×104[聚(L-丙交酯)].醇盐配体对聚合产物的分子量和分子量分布影响显著,随醇铁配体体积增大,聚合产物的分子量逐渐降低,分子量分布也逐渐加宽.1H和13C-NMR分析表明醇铁对L-丙交酯的开环聚合没有发生消旋化,对D,L-丙交酯的开环聚合有一定的等规加成选择性.MALDI-TOF MS分析指出D,L-丙交酯在开环聚合过程中发生了分子间的酯交换反应,用13C-NMR评价了各醇铁引发体系在聚合过程中的酯交换程度.但基于谱峰分辨原因,醇铁配体对立构加成选择性和酯交换的影响的规律性不明显.     

Photochemical reactions of high polymers. XIV. Syntheses and photochemical reactions of copolymers bearing O-acyloxime groups

Copolymers bearing pendant O-acyloxime groups were synthesized by two methods: copolymerizations of oxime acrylate (methyl β-naphthyl ketone oxime acrylate or benzophenone oxime acrylate) and styrene, condensation of acrylic acid—styrene copolymer with oximes (benzophenone oxime, p-nitrobenzophenone oxime, methyl β-naphthyl ketone oxime, benzalacetone oxime or 9-fluorenone oxime). The photochemical behavior of the O-acyloxime copolymers changed markedly with the irradiation conditions: irradiation of benzene solutions led to degradation in air and crosslinking under nitrogen, while irradiation of solid films in air resulted in simultaneous degradation and crosslinking. Photolysis of methyl β-naphthyl ketone oxime acetate, a model for the O-acyloxime copolymer, in benzene solution under nitrogen resulted in scission of the N? O bond. The same reaction was observed in the irradiation of the O-acyloxime copolymers. It is suggested that formation of free radicals on the polymer chains via scission of the N? O bond is followed by decarboxylation. In the absence of oxygen, crosslinking of the polymer by recombination of the free radicals competes with degradation via β-scission. In the presence of oxygen, autoxidative degradation predominates.     

Effect of primary radical termination on chain length and initiator efficiency

In polymerization with primary radical termination, when reaction between primary radicals, which escape from solvent cage, is not negligible, a relation between chain length and polymerization rate is found regardless of tractable approximate procedures. Such a relation is applied to the kinetic data obtained in the polymerizations of methyl methacrylate (MMA) and vinyl acetate (VA) initiated by 2,2′-azobis(2,4-valeronitrile) at 50.0°C. Further, when the primary radical termination is high, an initiator efficiency can not be approximated to a ratio of the primary radicals escaping from the cage to the total primary radicals formed in the cage. In the polymerization of MMA, after the primary radicals escapes from the cage, they immediately react with the monomer. Thus, the reaction between the primary radicals is not significant. However, in the polymerization of VA, the rate of reaction between the primary radical and the monomer might be comparable to the rate of reaction between the primary radicals when the initiator concentration is quite high.     

Grafting of polymers onto and/or from silica surface during the polymerization of vinyl monomers in the presence of γ‐ray‐irradiated silica

The effects of radicals on silica surface, which were formed by γ‐ray irradiation, on the polymerization of vinyl monomers were investigated. It was found that the polymerization of styrene was remarkably retarded in the presence of γ‐ray‐irradiated silica above 60 °C, at which thermal polymerization of styrene is readily initiated. During the polymerization, a part of polystyrene formed was grafted onto the silica surface but percentage of grafting was very small. On the other hand, no retardation of the polymerization of styrene was observed in the presence of γ‐ray‐irradiated silica below 50 °C; the polymerization tends to accelerate and polystyrene was grafted onto the silica surface. Poly(vinyl acetate) and poly(methyl methacrylate) (MMA) were also grafted onto the surface during the polymerization in the presence of γ‐ray‐irradiated silica. The grafting of polymers onto the silica surface was confirmed by thermal decomposition GC‐MS. It was considered that at lower temperature, the grafting based on the propagation of polystyrene from surface radical (“grafting from” mechanism) preferentially proceeded. On the contrary, at higher temperature, the coupling reaction of propagating polymer radicals with surface radicals (“grafting onto” mechanism) proceeded to give relatively higher molecular weight polymer‐grafted silica. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2972–2979, 2006     

Chain transfer for vinyl monomers polymerized in N-allylstearamide

Apparent transfer constants have been determined for styrene, methyl methacrylate vinyl acetate, and diethyl maleate polymerized in N-allylstearamide at 90°C. Regression coefficients for transfer were: methyl methacrylate, 0.301 × 10^?3; styrene, with no added initiator, 0.582 × 10^?3; styrene, initiated with benzoyl peroxide, 0.830 × 10^?3; vinyl acetate, 62.01 × 10^?3; and diethyl maleate, 2.24 × 10^?3. Rates of polymerization were retarded for both styrene and methyl methacrylate. Vinyl monomer and comonomer disappearance followed an increasing exponential dependence on both initiator and monomer concentration. Although degradative chain transfer probably caused most of the retardation, the cross-termination effect was not eliminated as a contribution factor. Rates for the vinyl acetate copolymerization were somewhat retarded, even though initiator consumption was large because of induced decomposition. The kinetic and transfer data indicated that the reactive monomers added radicals readily, but that rates were lowered by degradative chain transfer. Growing chains were terminated at only moderate rates of transfer. Unreactive monomers added radicals less easily, producing reactive radicals, which transferred rapidly, so that molecular weights were lowered precipitously. Although induced initiator decomposition occurred, rates were still retarded by degradative chain transfer. A simple empirical relation was found between the reciprocal number-average degree of polymerization, 1/X?_n1 and the mole fraction of allylic comonomer entering the copolymer F₂, which permitted estimation of the molecular weight of copolymers of vinyl monomers with allylic comonomers. This equation should be applicable when monomer transfer constants for each homopolymer are known and when osmometric molecular weights of one or two copolymers of low allylic content have been determined.     

十二烷基苯磺酸钡存在下负离子聚合控制聚苯乙烯立构规整性研究

以正丁基锂(n-BuLi)为引发剂,环已烷为溶剂,通过添加十二烷基苯磺酸钡/四氢呋喃(SDBB/THF),对苯乙烯负离子聚合进行了研究.该体系可在60℃聚合得到立构规整性聚苯乙烯,其丁酮不溶物含量可达80%左右.13C-NMR表征结果显示其微观序列组成以等规结构为主,三元组mm和等规五元组mmmm含量可达57%和45%;DSC谱图中不仅有聚苯乙烯玻璃化温度(100℃),而且在211℃有一熔融峰.GPC结果表明,实测分子量与设计分子量差别较大,且分子量分布较宽。     

Free-radical grafting of monomers to polydienes. I. Effect of reaction conditions on grafting of styrene to polybutadiene

The radical-induced grafting of styrene onto polybutadiene (PBD) in benzene solution at 60°C has been studied. Provided the PBD concentration is kept below about 1.0 monomermole/l. the polymerization of styrene shows normal kinetic behavior. The proportion of polystyrene incorporated as graft is independent of the initiator (benzoyl peroxide) concentration but increases as the ratio of PBD to styrene in the reaction medium increases. Azobisisobutyronitrile produces no graft copolymer in this system. It appears that the reaction leading to graft formation is direct attack of initiator radicals on the rubber, probably by a hydrogen-abstraction reaction.     

Two-Dimensional Chromatographic Analysis of Polystyrene-block-poly(methyl methacrylate) Copolymers Synthesized by Selective Oxidation of Polystrene-9-borabicyclo[3.3.1]nonane

Summary: The preparation of polystyrene block methyl methacrylate copolymers (PS-b-PMMA) is described. The polystyrene segment was prepared by anionic polymerization and the methylmethacrylate segment was prepared via free radical autoxidation of a borane agent attached to the styrene chain. 1 The chemistry involves a transformation of the anionic polymerization process to borane chemistry by firstly producing polystyrene with chain end unsaturated alkyl functional groups prepared using a n-butyllithium initiator and termination with allylchlorodimethylsilane. Secondly, the unsaturated macroinitiator end was hydroborated by 9-borabicyclo[3.3.1]nonane (9-BBN) to produce a borane terminated PS. Thirdly, the borane group at the chain end was selectively oxidized and converted to polymeric radicals in the presence of methyl methacrylate which then initiated radical polymerization to produce block copolymers. The polymer obtained was characterized using several chromatographic techniques including LC-CC (liquid chromatography under critical conditions) for the polystyrene segments and two-dimensional chromatography with LC-CC in the first dimension and SEC in the second. The results show that block formation was successful although significant homopolymerization of methyl methacrylate is also obtained.     

Novel synthesis of triblock PDMS-PS-PDMS copolymers

Benzyl 6-(2′-pentamethyldisiloxanyl ethyl)-ortho-tolyl ketone (I) was prepared by a ruthenium-catalyzed Murai reaction of benzyl ortho-tolyl ketone with vinyl pentamethyldisiloxane. The reaction of I with a mixture of styrene and a catalytic amount of picoline Cu(II) acetate yielded the telechelic polystyrene α,ω-bis(2-pentamethyl-disiloxanyl ethyl)polystyrene (III). The acid-catalyzed equilibration polymerization of octamethylcyclotetrasiloxane into the Si O Si bonds of telechelic III yielded the polydimethylsiloxane-polystyrene-polydimethylsiloxane triblock soft–hard–soft copolymer. The molecular weights of the copolymers were studied by ¹H NMR end-group analysis and gel permeation chromatography. The thermal properties and morphology of IV were examined by differential scanning calorimetry and transmission electron microscopy (TEM). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 482–488, 2000     

Preparation and characterization of a novel star ABC triblock copolymer of styrene,ethylene oxide,and methacrylic acid

The preparation of a star triblock copolymer based on polystyrene, poly(ethylene oxide), and poly(methacrylic acid) blocks (S-St-EO-MAA) is described. The polymer structure was achieved by the following route: the polystyrene macroanion (PS_m) was formed first by a butyllithium-initiated polymerization of styrene and capping with Michler's ketone; the resulting N,N,N′,N′-tetramethyl-4,4′-diaminodiphenylmethanol (TDDM)-terminated polystyrene was further reacted with metal potassium. The oxo-anion initiated the ring-opening polymerization of ethylene oxide, and the desired ABC triblock copolymer was obtained by precipitation polymerization of methacrylic acid (MAA) initiated with a charge transfer complex (CTC) under UV irradiation using benzene as a solvent. The complex is composed of PS-b-PEO with a TDDM end group (PS-b-PEO_tm) and benzophenone (BP).     

Studies on Mechanism of Grafting of Polystyrene on Elastomer Backbone

The mechanism of grafting of polystyrene on a polybutadiene (PB) backbone during the preparation of impact-resistant polystyrene was studied by withdrawing samples during propolym-erization from beginning of the reaction to about 25% conversion. Good separation of the “elastomer and graft” fraction of the polymer from the free polystyrene part could be achieved by using 0.24 volume fraction of methanol in (MEK + benzene) + methanol solvent-nonsolvent. IR analysis of the grafted fraction showed that the microstructure of the elastomer remained unaltered. The unsaturation of the samples studied through the bromine number as well as by the perbenzoic acid number was also found to remain unchanged. Formation of free polystyrene started with the onset of polymerization and was faster. During prepolymerization, 80% of styrene converted constantly to form free polystyrene and 20% went into the grafted polymer. The results indicate that grafting is initiated through proton abstraction at the α-carbon of butadiene, most probably by initiator radicals. The grafted polystyrene chains possibly are shorter than free polystyrene chains.